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The yeast Saccharomyces cerevisiae is the pre-eminent organism for the study of basic functions of eukaryotic cells¹. All of the genes of this simple eukaryotic cell have recently been revealed by an international collaborative effort to determine the complete DNA sequence of its nuclear genome. Here we describe some of the features of chromosome XII.

The complete nucleotide sequence of Saccharomyces cerevisiae chromosome VII has 572 predicted open reading frames (ORFs), of which 341 are new. No correlation was found between G+C content and gene density along the chromosome, and their variations are random. Of the ORFs, 17% show high similarity to human proteins. Almost half of the ORFs could be classified in functional categories, and there is a slight increase in the number of transcription (7.0 %) and translation (5.2 %) factors when compared with the complete S. cerevisiae genome. Accurate verification procedures demonstrate that there are less than two errors per 10,000 base pairs in the published sequence.

The complete DNA sequence of the yeast Saccharomyces cerevisiae chromosome IV has been determined. Apart from chromosome XII, which contains the 1–2 Mb rDNA cluster, chromosome IV is the longest S. cerevisiae chromosome. It was split into three parts, which were sequenced by a consortium from the European Community, the Sanger Centre, and groups from St Louis and Stanford in the United States. The sequence of 1,531,974 base pairs contains 796 predicted or known genes, 318 (39.9%) of which have been previously identified. Of the 478 new genes, 225 (28.3%) are homologous to previously identified genes and 253 (32%) have unknown functions or correspond to spurious open reading frames (ORFs). On average there is one gene approximately every two kilobases. Superimposed on alternating regional variations in G+C composition, there is a large central domain with a lower G+C content that contains all the yeast transposon (Ty) elements and most of the tRNA genes. Chromosome IV shares with chromosomes II, V, XII, XIII and XV some long clustered duplications which partly explain its origin.

This directory was made possible by a unique international collaboration between the 633 scientists whose names appear below. It represents both the first published description of the complete sequence of most chromsomes from Saccharomyces cerevisiae, and the first published overview of the entire sequence. As such, the authors would like future papers referring to the entire sequence and/or its contents to cite this directory; future papers referring to the sequence of individual chromosomes should refer to the papers listed at the head of page 9. The authors’ affiliations appear in the papers describing the individual chromosomes.

Quantum correlations between the laser beams and the positions of the 40-kg mirrors of LIGO are confirmed experimentally, enabling high-precision measurements of both gravitational waves and macroscopic quantum states.

Squeezed states of light have been experimentally demonstrated to improve the performance of the Laser Interferometer Gravitational-wave Observatory (LIGO) in astrophysically relevant frequency regions. This enhanced performance may help to reach the sensitivity required for detecting gravitational waves.

The astronomical event GW170817, detected in gravitational and electromagnetic waves, is used to determine the expansion rate of the Universe, which is consistent with and independent of existing measurements.

A stochastic background of gravitational waves is expected to arise from a superposition of a large number of unresolved gravitational-wave sources and should carry unique signatures from the earliest epochs of the Universe. Limits on the amplitude of the stochastic gravitational-wave background are now reported using the data from a two-year science run of the Laser Interferometer Gravitational-wave Observatory. These limits rule out certain models of early Universe evolution.

‘Squeezed light’ enables quantum noise in one aspect of light to be reduced by increasing the noise, or more accurately the quantum uncertainty, of a complementary aspect. This has now been used to push the detectors at the heart of the GEO600 gravitational wave observatory to unprecedented levels of sensitivity.